Observations, Ruminations, and Cantankerous Notions

Getting Steamed

I’ve never been impressed with journalists’ knowledge of how the world physically work. It can be overlooked when it involves specialized knowledge, such as the ins and outs of utility work. It’s harder when it involves basic science.

Such was a column in a local newspaper where a columnist moaned about the water used by coal-fired and nuclear generation, while hoping the state Powers that Be force utilities to use gas turbines. That gas turbines are much more expensive than coal and nuclear is perhaps specialized knowledge: Gas turbine plants ramp up quickly, but the energy produced is more expensive, which is why they’re used as “peaking” generation. That’s during times of peak use, when the wholesale price of electricity climbs to the point where gas generation is economical. Buta basic knowledge of how coal and nuclear power is turned into electricity is basic science, so basic that it goes all the way back to when Christianity was spreading from Judea and Galilee. It involves steam.

Whether you’re making electricity by burning coal or splitting atoms, the purpose is identical: to make steam, and then have the steam to turn the generators. We’re all familiar that boiling water turns into a gas – steam – and expands, and that expansion is how we can make it do work. Steam power goes all the way back to the 1st Century AD, though it was only used for a few small applications thereafter. The first real steam engine didn’t appear until the late 17th Century.

Until the mid 18th Century, steam engines all operated by venting the spent steam into the air, which meant the boilers had to be constantly filled with new water. Then James Watt hit on the idea of the condenser, cooling the used steam for greater efficiency and reuse. This make steam engines much more efficient. Steam engines that vented to the air would continue to be used where weight and power was an issue, which is why the old steam locomotives had to take on water, but closed steam engines, where the water used for steam is cooled and reused, would come to dominate stationary applications. This included mines, factories, and later, electric generation.

From the 17th Century through the 19th, steam engines used pistons to produce power. But in 1884, Charles Parsons invented the first modern steam turbine engine and used it to generate electricity. Turbines are more efficient than piston in turning steam into rotary motion, and is why both coal and nuclear generators today use steam turbines.

Steam turbine generators are closed steam engines, so the water that turns the turbines is cooled and reused. In a coal-fired plant, this is done by drawing in water from a lake or a river, cooling the condenser, running it through cooling towers to further reduce the temperature, and discharging it back into the lake or river. Nuclear power plants used two closed system. A closed system from the reactor heats a closed system that drives the turbine, and then lake or river water is used condense the steam back into water. Then, just like a coal-fired plant, this water is run through a cooling tower to further reduce the temperature, and is then discharged back into the lake or river.

The key thing to remember about both is they do not consume the water used to cool the turbine steam. So, even though the newspaper column implied coal and nuclear plants “use up” this water, they don’t. They heat it, and there are laws in place to determine how hot the water is when it’s returned to the environment, but they don’t convert it to steam and discharge it into the atmosphere.

If you’ve ever seen power plant cooling towers, you know that sometimes there seems to be steam coming from then. That’s condensation of the moisture already in the air and not steam. It can be quite impressive at times. Yet the water taken from the river or lake goes right back into it again.

This is all basic stuff. While we might forget some things we learned in science class, you don’t have to look far on the Internet to find a diagram of how power plants work.